In the case of a timepiece, such as a mechanical watch, an acoustic signature or acoustic hallmark consists in studying the noises generated by the escapement. To perform this type of measurement, it is sufficient to position the cased watch on a fitting stand, which is always identical, and to record the sound emitted over time by an aerial or contact microphone. The time signal is then analysed to detect the occurrence of shocks and frictions. These measurements are performed to check the chronometric performances of the mechanical movement and to identify operating defects. There are commercial devices which automatically perform this type of measurement. They are for example produced by Witschi Electronic AG.
To the Applicant's knowledge, these measurements have never been adapted and utilised for detecting any counterfeiting of a timepiece. The reason for this is that the analysis generally does not take account of the specific frequency content of the generated noise. Further, depending on the various systems for measuring the noises generated by a mechanical watch movement, it is difficult to extract behaviour patterns, which are repeated, for different mechanical movements of perfectly identical design. It is to be noted that the simple fact of removing and recasing the same mechanical movement in the watch case is liable to modify certain features, such as the peak shock level. The position of a contact or aerial microphone may also be a source of strong variations in basic acoustic signature indicators. This means that it is not possible to differentiate each watch tested so that it can be precisely identified either as a specific calibre, or as a specific piece.